if you do the arithmetic and figure out how fast the patch is spinning when it exits the barrel, you'll see that it spreads out into the atmosphere and is left behind by the ball in what is most probably a matter of milliseconds ... think of a parachute deployment, only at a zillion times normal speed.
therefore, the shape of the patch isn't going to have an effect on the path of the ball on it's way to the target.
now, you may, if you want, spend a great deal of energy and time researching this problem, but I would recommend a method which is more fun and will provide you the results in which you will have the most confidence:
try it for yourself. if you do this, you'll have a great excuse to go to the range and shoot ("Are you going to shoot that stupid gun again?" ... "I've got to do some testing. honey, i'll be back by lunchtime... " - ok - I don't eat lunch at four in the afternoon either... )
AND
you won't have to spend a bunch of your valuable time listening to pontificators (like, for instance, me) and that's even more time you get to spend at the range...
betcha a case of beer you get the same result with round as you do with square as you do with cut at the muzzle.
(I cut mine at the muzzle, but that's only 'cause I think it looks cool)
there you go: free advice, and no doubt well worth the price.
Make good smoke! :v